A31418 — Encoder 1: Speed change not plausible (alarm)

A31418 tells you that the speed actual value of Encoder 1 — an HTL/TTL square-wave encoder — has changed faster than the drive allows. The manuals print the code as Encoder 1: Speed change not plausible (alarm) and, in the G130/G150 manual, as Encoder 1: Speed difference per sampling rate exceeded. In both cases the measured speed change is compared with the threshold in p0492: the S120/S150 manual describes the threshold being exceeded over several sampling cycles, while the G130/G150 manual describes the speed difference between two sampling cycles exceeding p0492. Where an averaged speed actual value is used, its change is additionally monitored in the current controller sampling time. Depending on how the drive is configured, the same condition can also be output as a fault (F) or without any reaction (N).

• For an HTL/TTL encoder, the speed change has exceeded the value in p0492 — described as the change over several sampling cycles (S120/S150 wording) or as the speed difference between two sampling cycles (G130/G150 wording).
• Where an averaged speed actual value exists, the change to this averaged value is also monitored in the current controller sampling time and is covered by the same monitoring.

1. Check the tachometer feeder cable for interruptions.
2. Check the grounding of the tachometer shielding.
3. If required, increase the setting of p0492 — this is the threshold the speed monitoring compares against, so raising it widens the tolerated speed difference per sampling cycle.

• The Message value (%1) is the alarm value, which the drive also stores in r2124. Interpret it as a decimal number; the manual gives no decoding, because it is only for internal Siemens troubleshooting.

• p0492 — maximum velocity difference per sampling cycle for a square-wave encoder: the threshold that Encoder 1's speed change is monitored against; the remedy is to increase this setting if required.
• r2124 — alarm value: read the alarm value of A31418 here and interpret it as a decimal number.

As an alarm, A31418 requires no acknowledgement and the drive takes no automatic response — the alarm clears itself once the speed actual value becomes plausible again. If the drive is configured to output the same condition as a fault, that fault must be acknowledged immediately before the drive can be restarted.